1. Field of the Invention
This invention relates to a semiconductor washing solution and a method of producing a semiconductor device using the semiconductor washing solution, and more particularly to a semiconductor washing solution which is used to remove various fine particles sticking to a semiconductor substrate in a process of production of a semiconductor device and a method of producing a semiconductor device using the semiconductor washing solution.
2. Description of the Related Art
While a semiconductor device is formed by repeating various steps of film formation, photo-lithography, etching, oxidation, heat treatment and so forth, a semiconductor substrate is subject to various contaminations in the production steps. Therefore, between each adjacent steps, washing for removing contaminations is performed. However, as a tendency of increase in scale and refinement of semiconductor devices is exhibited in recent years, the influence of contamination upon a device characteristic has been and is increasing. Thus, it progressively becomes important to remove foreign articles or contaminations to the utmost from semiconductor devices.
Among various contaminations, the contamination of fine particles occurs in the steps of transportation, film formation, dry etching and so forth. Since the contamination of fine particles has a significant influence upon the yield of semiconductor device, it is desired to remove the contamination of fine particles completely. However, it is difficult to remove fine particles sticking to fine recessed portions such as, for example, contact holes by rinsing with water or washing with a gas-phase washing agent. Therefore, it is a common practice to perform washing, after a step of film formation or dry etching in which particle contamination is liable to occur, using a mixed solution of ammonium hydroxide, hydrogen peroxide and water (NH4OH:H2O2:H2O) (the solution is hereinafter referred to as APM) which has a high fine particle removing capacity.
For example, referring to FIGS. 5(a) and 5(b), a doped oxide film (PSG, BPSG or the like) 2, a non-doped oxide film (NSG) 3, another doped oxide film 4 and another non-doped oxide film 5 are deposited as an inter-layer insulating film on a silicon substrate 1, and a contact hole 6 for exposing the surface of the substrate 1 therethrough is perforated as seen FIG. 5(a) using a photo-lithography method and a dry etching method and then APM washing is performed (refer to FIG. 5(b)). Thereafter, a metal film for filling up the contact hole 6 is deposited, for example, by a CVD method.
For the APM used for the washing operation of the type mentioned, an APM whose composition ratio is NH4OH:H2O2:H2O=x:y:20 (x=0.01 to 5 and y=0.1 to 4) or the like is used normally, and is used in a temperature range from 60° C. to 80° C. The processing time of the substrate is approximately 4 minutes to 20 minutes.
Since the conventional APM described above exhibits a higher etching rate for a doped oxide film than for a non-doped oxide film, if washing is performed using the processing solution for a contact hole provided in an inter-layer insulating film formed from a non-doped oxide film and a doped oxide film layered on each other, unevenness or offsets are formed on an inner wall of a contact hole as seen in FIG. 5(b). If such unevenness appears, then it is impossible to fill up the hole completely with a plug material, and this gives rise to production of a void.
Further, since the conventional APM exhibits a high etching rate, disconnection of a wiring line is caused by reduction of the film thickness of the wiring line or occurrence of incomplete contact is sometimes invited by the loss of a conductive film at a bottom portion of a contact hole.
In this manner, a harmful influence that unevenness or offsets are produced or reduction of a film thickness is caused by APM washing is described in a journal of a society, Study of Aerosol, 1996, Vol. 11(1), No. 8–15, pp.8–13, particularly in connection with FIG. 8.
Further, since the conventional APM is used at a temperature higher than 60° C., ammonia which has a comparatively high vapor pressure vaporizes comparatively quickly. Such vaporization of ammonia varies the composition of the APM and drops the washing capacity of the APM. In order to compensate for such vaporization of the APM to eliminate the drop of the washing capacity, an ammonia solution must be supplemented frequently (after each several minutes) to keep the composition ratio fixed.